The present disclosure relates to power storage devices, power storage methods, and programs.
In recent years, secondary batteries that can be used many times after being repeatedly recharged have been widely used as power sources for mobile terminal devices such as cellular phones and laptop computers. On the other hand, electric power generation from renewable energy sources, that is, natural energy sources such as sunlight, wind power, and geothermal heat have been attracting attention from the viewpoint of global environmental conservation and CO2 emission reduction. It is not easy to supply stable electric power using these natural energy sources because the amount of energy obtainable from these natural energy sources constantly varies depending on natural conditions such as the amount of sunlight and the force of wind. Therefore, some effort has been made to supply stable electric power by outputting uniform electric power with the use of a combination of secondary batteries and natural energy sources.
In addition to the above-mentioned usage, a secondary battery is expected to be widely used in various other applications. However, there is a problem in that a secondary battery deteriorates after repeated charge-discharge operations, with the result that the voltage and electric energy of the secondary battery decrease.
A power storage system that prevents a secondary battery from being charged with an excessively high charging current and increases the life of the secondary battery is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2010-41883. To put it concretely, according to the power storage system described in Japanese Unexamined Patent Application Publication No. 2010-41883, a period during which an amount of charge electric energy in the power storage system increases is determined, as a restrictive period during which a charging current value has to be limited, on the basis of remaining amount of electric energy of a battery, consumption patterns of power consumed by loads, and power generation prediction patterns, and the charging current value during the restrictive period is calculated. Therefore, the battery is prevented from being charged with an excessively high charging current and the life of the battery can be prolonged.
In addition, a method in which an optimization plan that optimizes a charged state of a secondary battery on the basis of a user's schedule is disclosed in Japanese Unexamined Patent Application Publication No. 2004-94607. To put it concretely, a method in which the deterioration of a secondary battery owing to continuous charging of the secondary battery can be suppressed is disclosed in Japanese Unexamined Patent Application Publication No. 2004-94607. The suppression of the deterioration is achieved by keeping the secondary battery in a full-charge state only at the time near to a period during which the secondary battery is supposed to be continuously used for a long time, and by keeping the secondary battery in a charged state that is lower than the full-charge state during a period in which the secondary battery and an external power source are used in parallel for a long time.